CCNA Cisco Certified Network Associate Study Guide - FTP Server

� The best route to each remote network
� How to maintain and verify routing information
The IP Routing Process 237
The router learns about remote networks from neighbor routers or from
an administrator. The router then builds a routing table that describes how
to find the remote networks. If the network is directly connected, then the
router already knows how to get to the network. If the networks are not
attached, the router must learn how to get to the remote network with either
static routing, which means that the administrator must hand-type all network
locations into the routing table, or use dynamic routing. Dynamic
routing is the process of routing protocols running on the router communicating
with neighbor routers. The routers then update each other about all
the networks they know about. If a change occurs in the network, the
dynamic routing protocols automatically inform all routers about the
change. If static routing is used, the administrator is responsible for updating
all changes by hand into all routers.
The IP Routing Process
The IP routing process is fairly simple and doesn’t change, regardless
of the size of network you have. For an example, we’ll use Figure 5.1 to
describe step by step what happens when Host A wants to communicate with
Host B on a different network.
FIGURE 5.1 IP routing example using two hosts and one router
>ping 172.16.20.2
Host A
172.16.10.2
E0: 172.16.10.1 E0: 172.16.20.1
Host A
172.16.20.2